Various disklike data storage media, including CDs and DVDs to read and write data using a light beam, Floppy™ disks to read and write data using magnetism, and MOs and MDs to read and write data using a light beam and magnetism in combination, have already been used extensively around the world. Among other things, DVD-RAMs, MOs and other rewritable media are housed in a protective casing such as the one disclosed in Patent Document No. 1 in order to protect the data stored there.
FIG. 47 is a perspective view schematically illustrating the disk cartridge that is disclosed in Patent Document No. 1. As shown in FIG. 47, the disk cartridge 100 includes a supporting base member 101 that houses a disk 10, which is a read-only or rewritable data storage medium, and that forms the outer shell of the disk cartridge 100.
The supporting base member 101 consists of an upper housing 101a and a lower housing 101b, which are joined together to store the disk 10 inside.
The supporting base member 101 has a window 101w to allow some means for rotating the disk 10 (such as a spindle motor) and read/write means such as an optical head to enter the supporting base member 101 and access the disk 10. The window 101w has been cut through the principal surfaces of the upper and lower housings 101a and 101b and the disk 10 housed in the supporting base member 101 is exposed through the window 101w. 
The disk cartridge 100 includes a cartridge shutter 103 that has been folded in a C-shape to close the window 101w on the upper and lower surfaces of the supporting base member 101 and to sandwich the supporting base member 101 and protect the data side of the disk 10 to be exposed inside the window 101w. 
The cartridge shutter 103 can move parallel in the direction indicated by the arrow P in FIG. 47 and is biased by a spring so as to keep the window 101w closed. Thus, this disk cartridge 100 is designed so as not to expose the disk 10 inside the window 101w unless some external force is applied to the cartridge shutter 103.
The supporting base member 101 further includes a bridge portion 104 that bridges an outer side of the window 101w. The bridge portion 104 not only maintains the rigidity of the supporting base member 101 but also guides the cartridge shutter 103 in the direction indicated by the arrow P.
With this cartridge shutter 103, the disk cartridge 100 prevents dust from entering the disk cartridge 100 being carried through the window 101w and also prevents the user from leaving a fingerprint on the disk 10.
To load this disk cartridge 100 into a disk drive and to read/write data from/on the disk 10, the disk needs to be clamped and rotated by the spindle motor and the optical head needs to access the disk 10. For that purpose, as the disk cartridge 100 being inserted into the disk drive goes in the direction indicated by the arrow Q, the notched portion 103a of the cartridge shutter 103 gets engaged with the protrusion 104a of a shutter opener 104 and the shutter opener 104 is turned around the center of rotation 104b in the direction indicated by the arrow R, thereby sliding the cartridge shutter 103 in the direction indicated by the arrow P as shown in FIG. 48. As a result, the cartridge shutter 103 can be opened and the disk 10 can be exposed through the window 101w.                 Patent Document No. 1: Japanese Patent Application Laid-Open Publication No. 9-153264        